1. Field of the Invention
The present invention relates to a solenoid actuated valve device and more particularly to a solenoid actuated valve device for controlling the flow of fluid in proportion to the electric current supplied to the solenoid coil.
2. Prior Art
A conventional solenoid actuated valve device is comprised of a linear motor of the movable coil type and a valve means. The linear motor includes a core, a bobbin slidably mounted on the core, a solenoid coil wound on the bobbin, permanent magnets mounted adjacent the solenoid coil so that the magnetic flux of each magnet intersects the winding of the solenoid coil at right angles thereto, and a yoke or body forming a magnetic circuit with the core. The valve means in general includes a sliding valve member which slides with the bobbin on the core in response to an electric current flowing through the solenoid coil to thereby proportionally control the opening and closing of apertures formed in the core between an inlet port and an outlet port.
In such prior solenoid actuated valves, it is desirable that the clearance between the core and the permanent magnet be as small as possible to thereby increase the magnetic force acting on the bobbin. However, as the clearance is reduced, one chamber at the side of the inlet and outlet ports which is defined by the magnets, bobbin, core and the like is substantially isolated from the other chamber which is defined at the opposite side of said valve device by means of the magnets and the like. Therefore, when the bobbin is moved in a direction where the bobbin allows fluid communication between the inlet and outlet ports the volume of the other chamber is reduced and the fluid within the other chamber is compressed and pressurized. When the bobbin is moved in the opposite direction, the volume of the other chamber is increased and the fluid pressure within the other chamber is reduced. Thus, a differential in fluid pressure is created between the chambers on opposite sides of the permanent magnets in response to movement of the bobbin. Thus, the bobbin is urged by this differential in fluid pressure and the bobbin movements are not precisely controlled in proportion to the electric current supplied to the solenoid coil on the bobbin. Thus, the desired accurate control of the flow of fluid from the inlet port to the outlet port cannot be achieved.